Re: [PATCH 2/7] dma-buf: add dma_fence_chain_alloc/free

[Christian König <ckoenig.leichtzumerken@xxxxxxxxx>]

Am 11.06.21 um 09:54 schrieb Daniel Vetter:
> On Thu, Jun 10, 2021 at 11:17:55AM +0200, Christian König wrote:
> > Add a common allocation helper. Cleaning up the mix of kzalloc/kmalloc
> > and some unused code in the selftest.
> >
> > Signed-off-by: Christian König <christian.koenig@xxxxxxx>
> > ---
> >   drivers/dma-buf/st-dma-fence-chain.c          | 16 ++++----------
> >   drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c        |  4 ++--
> >   drivers/gpu/drm/drm_syncobj.c                 |  6 ++---
> >   .../gpu/drm/i915/gem/i915_gem_execbuffer.c    |  6 ++---
> >   drivers/gpu/drm/msm/msm_gem_submit.c          |  6 ++---
> >   include/linux/dma-fence-chain.h               | 22 +++++++++++++++++++
> >   6 files changed, 35 insertions(+), 25 deletions(-)
> >
> > diff --git a/drivers/dma-buf/st-dma-fence-chain.c b/drivers/dma-buf/st-dma-fence-chain.c
> > index 9525f7f56119..8ce1ea59d31b 100644
> > --- a/drivers/dma-buf/st-dma-fence-chain.c
> > +++ b/drivers/dma-buf/st-dma-fence-chain.c
> > @@ -58,28 +58,20 @@ static struct dma_fence *mock_fence(void)
> >   	return &f->base;
> >   }
> >   
> > -static inline struct mock_chain {
> > -	struct dma_fence_chain base;
> > -} *to_mock_chain(struct dma_fence *f) {
> > -	return container_of(f, struct mock_chain, base.base);
> > -}
> > -
> >   static struct dma_fence *mock_chain(struct dma_fence *prev,
> >   				    struct dma_fence *fence,
> >   				    u64 seqno)
> >   {
> > -	struct mock_chain *f;
> > +	struct dma_fence_chain *f;
> >   
> > -	f = kmalloc(sizeof(*f), GFP_KERNEL);
> > +	f = dma_fence_chain_alloc();
> >   	if (!f)
> >   		return NULL;
> >   
> > -	dma_fence_chain_init(&f->base,
> > -			     dma_fence_get(prev),
> > -			     dma_fence_get(fence),
> > +	dma_fence_chain_init(f, dma_fence_get(prev), dma_fence_get(fence),
> >   			     seqno);
> >   
> > -	return &f->base.base;
> > +	return &f->base;
> >   }
> >   
> >   static int sanitycheck(void *arg)
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
> > index 90136f9dedd6..325e82621467 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
> > @@ -1124,7 +1124,7 @@ static int amdgpu_cs_process_syncobj_timeline_out_dep(struct amdgpu_cs_parser *p
> >   
> >   		dep->chain = NULL;
> >   		if (syncobj_deps[i].point) {
> > -			dep->chain = kmalloc(sizeof(*dep->chain), GFP_KERNEL);
> > +			dep->chain = dma_fence_chain_alloc();
> >   			if (!dep->chain)
> >   				return -ENOMEM;
> >   		}
> > @@ -1132,7 +1132,7 @@ static int amdgpu_cs_process_syncobj_timeline_out_dep(struct amdgpu_cs_parser *p
> >   		dep->syncobj = drm_syncobj_find(p->filp,
> >   						syncobj_deps[i].handle);
> >   		if (!dep->syncobj) {
> > -			kfree(dep->chain);
> > +			dma_fence_chain_free(dep->chain);
> >   			return -EINVAL;
> >   		}
> >   		dep->point = syncobj_deps[i].point;
> > diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
> > index fdd2ec87cdd1..1c5b9ef6da37 100644
> > --- a/drivers/gpu/drm/drm_syncobj.c
> > +++ b/drivers/gpu/drm/drm_syncobj.c
> > @@ -861,7 +861,7 @@ static int drm_syncobj_transfer_to_timeline(struct drm_file *file_private,
> >   				     &fence);
> >   	if (ret)
> >   		goto err;
> > -	chain = kzalloc(sizeof(struct dma_fence_chain), GFP_KERNEL);
> > +	chain = dma_fence_chain_alloc();
> >   	if (!chain) {
> >   		ret = -ENOMEM;
> >   		goto err1;
> > @@ -1402,10 +1402,10 @@ drm_syncobj_timeline_signal_ioctl(struct drm_device *dev, void *data,
> >   		goto err_points;
> >   	}
> >   	for (i = 0; i < args->count_handles; i++) {
> > -		chains[i] = kzalloc(sizeof(struct dma_fence_chain), GFP_KERNEL);
> > +		chains[i] = dma_fence_chain_alloc();
> >   		if (!chains[i]) {
> >   			for (j = 0; j < i; j++)
> > -				kfree(chains[j]);
> > +				dma_fence_chain_free(chains[j]);
> >   			ret = -ENOMEM;
> >   			goto err_chains;
> >   		}
> > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> > index 66789111a24b..a22cb86730b3 100644
> > --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> > +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> > @@ -2983,7 +2983,7 @@ __free_fence_array(struct eb_fence *fences, unsigned int n)
> >   	while (n--) {
> >   		drm_syncobj_put(ptr_mask_bits(fences[n].syncobj, 2));
> >   		dma_fence_put(fences[n].dma_fence);
> > -		kfree(fences[n].chain_fence);
> > +		dma_fence_chain_free(fences[n].chain_fence);
> >   	}
> >   	kvfree(fences);
> >   }
> > @@ -3097,9 +3097,7 @@ add_timeline_fence_array(struct i915_execbuffer *eb,
> >   				return -EINVAL;
> >   			}
> >   
> > -			f->chain_fence =
> > -				kmalloc(sizeof(*f->chain_fence),
> > -					GFP_KERNEL);
> > +			f->chain_fence = dma_fence_chain_alloc();
> >   			if (!f->chain_fence) {
> >   				drm_syncobj_put(syncobj);
> >   				dma_fence_put(fence);
> > diff --git a/drivers/gpu/drm/msm/msm_gem_submit.c b/drivers/gpu/drm/msm/msm_gem_submit.c
> > index 5480852bdeda..6ff6df6c4791 100644
> > --- a/drivers/gpu/drm/msm/msm_gem_submit.c
> > +++ b/drivers/gpu/drm/msm/msm_gem_submit.c
> > @@ -586,9 +586,7 @@ static struct msm_submit_post_dep *msm_parse_post_deps(struct drm_device *dev,
> >   				break;
> >   			}
> >   
> > -			post_deps[i].chain =
> > -				kmalloc(sizeof(*post_deps[i].chain),
> > -				        GFP_KERNEL);
> > +			post_deps[i].chain = dma_fence_chain_alloc();
> >   			if (!post_deps[i].chain) {
> >   				ret = -ENOMEM;
> >   				break;
> > @@ -605,7 +603,7 @@ static struct msm_submit_post_dep *msm_parse_post_deps(struct drm_device *dev,
> >   
> >   	if (ret) {
> >   		for (j = 0; j <= i; ++j) {
> > -			kfree(post_deps[j].chain);
> > +			dma_fence_chain_free(post_deps[j].chain);
> >   			if (post_deps[j].syncobj)
> >   				drm_syncobj_put(post_deps[j].syncobj);
> >   		}
> > diff --git a/include/linux/dma-fence-chain.h b/include/linux/dma-fence-chain.h
> > index 9d6a062be640..5f45689a6d2e 100644
> > --- a/include/linux/dma-fence-chain.h
> > +++ b/include/linux/dma-fence-chain.h
> > @@ -12,6 +12,7 @@
> >   
> >   #include <linux/dma-fence.h>
> >   #include <linux/irq_work.h>
> > +#include <linux/slab.h>
> >   
> >   /**
> >    * struct dma_fence_chain - fence to represent an node of a fence chain
> > @@ -53,6 +54,27 @@ to_dma_fence_chain(struct dma_fence *fence)
> >   	return container_of(fence, struct dma_fence_chain, base);
> >   }
> >   
> > +/**
> > + * dma_fence_chain_alloc
> > + *
> > + * Returns a new dma_fence_chain object
> ... or NULL on failure.
>
> > + */
> > +static inline struct dma_fence_chain *dma_fence_chain_alloc(void)
> > +{
> > +	return kmalloc(sizeof(struct dma_fence_chain), GFP_KERNEL);
> > +};
> > +
> > +/**
> > + * dma_fence_chain_free
> > + * @chain: chain node to free
> > + *
> > + * Frees up an allocated but not used dma_fence_chain node.
> > + */
> > +static inline void dma_fence_chain_free(struct dma_fence_chain *chain)
> > +{
> > +	kfree(chain);
> kfree_rcu, and I guess this means this patch here should be cc: stable.

Nope, kfree() is correct here.

This is to free up fences which never been initialized, so an RCU grace 
period isn't necessary because nobody could potentially have a reference.

Christian.

> This is kinda why I'm questioning whether this "dma_fence are protected by
> rcu" cross driver api is really a good idea. We largely get it wrong in
> the details in a _ton_ of places.
>
> With the details fixed:
>
> Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
>
> > +
> >   /**
> >    * dma_fence_chain_for_each - iterate over all fences in chain
> >    * @iter: current fence
> > --
> > 2.25.1

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